We have studied the internal magnetic order of 3-nm (Fe 0.69Co 0.31) 0.6B 0.4 amorphous nanoparticles. These nanoparticles were dispersed in a non-magnetic matrix (non-interacting nanoparticles) to contrast them with the powder samples, where strong interparticle interactions are present. In similar fashion to the bulk alloy, this system exhibits a saturation magnetization maximum as a function of Fe composition near 69 at% Fe for the powder and dispersed samples at all temperatures. The saturation magnetization ( MS) of the dispersed sample shows anomalous behavior, revealing frustration in the internal magnetic order of the particles. Unexpectedly, the MS of the non-interacting sample at low temperatures is larger than the corresponding bulk alloy or the calculated value of MS for the same Fe-Co composition. By contrast, the powder sample has low MS values and it is approximately constant in temperature.
References
[1]
Chikazumi, S. Physics of Magnetism; Krieger Publ. Co.: Malabar, FL, USA, 1964; Chapter 4.
[2]
Dorman, J.L.; Fiorani, D. Magnetic Properties of Fine Particles; North-Holland: Amsterdam, The Netherlands, 1992.
[3]
Hadjipanayis, G.C.; Prinz, G.A. Science and Technology of Nanostructurated Materials; Plenum Press: New York, NY, USA, 1991.
[4]
Fiorani, D. Surface Effects in Magnetic Nanoparticles; Springer: New York, NY, USA, 2005.
[5]
Kodama, R.H.; Makhlouf, S.A.; Berkowitz, A.E. Finite size effects in antiferromagnetic NiO nanoparticles. Phys. Rev. Lett. 1997, 79, 1393–1396, doi:10.1103/PhysRevLett.79.1393.
[6]
García del Muro, M.; Batlle, X.; Labarta, A. Erasing the glassy state in magnetic fine particles. Phys. Rev. B 1999, 59, 13584–13587.
[7]
Martínez, B.; Obradors, X.; Balcells, L.; Rouanet, A.; Monty, C. Low temperature surface spin-glass transition in γ- Fe2O3 nanoparticles. Phys. Rev. Lett. 1998, 80, 181–184, doi:10.1103/PhysRevLett.80.181.
[8]
Batlle, X.; García del Muro, M.; Labarta, A. Interaction effects and energy barrier distribution on the magnetic relaxation of nanocrystalline hexagonal ferrites. Phys. Rev. B 1997, 55, 6440–6445.
[9]
Dormann, J.L.; Cherkaoui, R.; Spinu, L.; Nogués, M.; Lucari, F.; D’Orazio, F.; Fiorani, D.; García, A.; Tronc, E.; Jolivet, J.P. From pure superparamagnetic regime to glass collective state of magnetic moments in γ-Fe2O3 nanoparticle assemblies. J. Magn. Magn. Mater. 1998, 187, L139–L144, doi:10.1016/S0304-8853(98)00135-8.
[10]
M？rup, S.; Tronc, E. Superparamagnetic relaxation of weakly interacting particles. Phys. Rev. Lett. 1994, 72, 3278–3281, doi:10.1103/PhysRevLett.72.3278.
[11]
Jonsson, P.; Nordblad, P. Comment on “Erasing the glassy state in magnetic fine particles”. Phys. Rev. B 2000, 62.
[12]
Kodama, R.H.; Berkowitz, A.E. Atomic-scale magnetic modeling of oxide nanoparticles. Phys. Rev. B 1999, 59, 6321–6336.
[13]
Kachkachi, H.; Ezzir, A.; Nogués, M.; Tronc, E. Surface effects in nanoparticles: Application to maghemite γ-Fe2O3. Eur. Phys. J. B 2000, 14, 681–689, doi:10.1007/s100510051079.
[14]
Kachkachi, H.; Nogués, M.; Tronc, E.; Garanin, D.A. Finite-size versus surface effects in nanoparticles. J. Magn. Magn. Mater. 2000, 221, 158–163, doi:10.1016/S0304-8853(00)00390-5.
[15]
Iglesias, O.; Labarta, A. Finite-size and surface effects in maghemite nanoparticles: Monte Carlo simulations. Phys. Rev. B 2001, 63.
[16]
De Biasi, E.; Ramos, C.A.; Zysler, R.D.; Romero, H. Large surface magnetic contribution in amorphous ferromagnetic nanoparticles. Phys. Rev. B 2002, 65.
[17]
Zysler, R.D.; Romero, H.; Ramos, C.A.; de Biasi, E.; Fiorani, D. Evidence of large surface effects in Co-Ni-B amorphous nanoparticles. J. Magn. Magn. Mater. 2003, 266, 233–242, doi:10.1016/S0304-8853(03)00486-4.
[18]
De Biasi, E.; Ramos, C.A.; Zysler, R.D.; Romero, H.; Fiorani, D. Size dependence of the spin-flop transition in hematite nanoparticles. Phys. Rev. B 2005, 71.
[19]
De Biasi, E.; Ramos, C.A.; Zysler, R.D.; Fiorani, D. Metropolis algorithm for simulating hysteresis in ferromagnetic nanoparticles. Phys. B 2006, 372, 345–349, doi:10.1016/j.physb.2005.10.082.
[20]
Halperin, W.P. Quantum size effects in metal particles. Rev. Mod. Phys. 1986, 58, 533–606, doi:10.1103/RevModPhys.58.533.
[21]
Molina Concha, B.; Zysler, R.D.; Romero, H. Magnetization enhancement in Fe-Co-B alloy nanoparticles. Phys. B 2006, 384, 274–276, doi:10.1016/j.physb.2006.06.009.
[22]
Zysler, R.D.; Ramos, C.A.; Romero, H.; Ortega, A. Chemical synthesis and characterization of amorphous Fe-Ni-B magnetic nanoparticles. J. Mater. Sci. 2001, 36, 2291–2294, doi:10.1023/A:1017524923761.
[23]
Molina Concha, B.; Zysler, R.D.; Troiani, H.; Romero, H. Surface and local anisotropy effect in the magnetic order of Fe-Co-B nanoparticles. Phys. B 2004, 354, 121–124, doi:10.1016/j.physb.2004.09.032.
[24]
Molina Concha, B.; de Biasi, E.; Zysler, R.D. Monte Carlo simulation of Fe-Co amorphous nanoparticles magnetization. Phys. B 2008, 403, 390–393, doi:10.1016/j.physb.2007.08.057.
[25]
Zysler, R.D.; Fiorani, D.; Testa, A.M. Investigation of magnetic properties of interacting α-Fe2O3 nanoparticles. J. Magn. Magn. Mater. 2001, 224, 5–11, doi:10.1016/S0304-8853(00)01328-7.
[26]
Zysler, R.D.; Ramos, C.A.; De Biasi, E.; Romero, H.; Ortega, A.; Fiorani, D. Effect of interparticle interactions in (Fe0.26Ni0.74)50B50 magnetic nanoparticles. J. Magn. Magn. Mater. 2000, 221, 37–44, doi:10.1016/S0304-8853(00)00368-1.
[27]
Hansen, M.; Anderko, K. Constitution of Binary Alloys; McGraw Hill: New York, NY, USA, 1953.
[28]
De Biasi, E.; Ramos, C.A.; Zysler, R.D.; Romero, H. Magnetization enhancement at low temperature due to surface ordering in Fe-Ni-B amorphous nanoparticles. Phys. B 2002, 320, 203–205, doi:10.1016/S0921-4526(02)00682-8.
